One of conventional drive mechanisms for articulated portions of an articulated robot is disclosed, for example, in Japanese Laid-Open (Kokai) Patent Application No. 58-181586, and this will now be described with reference to the drawings. FIG. 1 is a front-elevational view of this conventional example, FIG. 2 is a side-elevational view thereof, and FIG. 3 is a detailed cross-sectional view of an articulation drive portion, indicated by a portion A in FIG. 1, for first and second arms serving as control arms. In these Figures, numeral (1) denotes a stationary base, numeral (2) a turntable turnable on the stationary base (2), numeral (3) a base fixedly mounted on the turntable (2), numeral (4) a first arm swingingly movable about a point (5) on the base (3), numeral (6) a first motor for driving the first arm (4), numeral (7) a second arm swingingly movable about a point (8) on the first arm (4), numerals (9) and (10) a link and a link support which cooperate with the first arm (4) and the second arm (7) to constitute a parallel link, numeral (11) a second motor for driving the second arm (7) through the link support (10) and the link (9), and numeral (12) a wrist mounted on a distal end of the second arm (7) for bending and twisting movements in directions indicated by arrows B and C.
Therefore, in this robot, the first arm (4) is swingingly moved forwardly and rearwardly by operating the first motor (6), and by operating the second motor (11), the link support (10) is swingingly moved upwardly and downwardly so that the second arm (7) is swingingly moved upwardly and downwardly about the center (8) of rotation through the parallel link mechanism comprising the first arm (4), the link (9) and the second arm (7). In other words, by controlling the first motor (6) and the second motor (11), the wrist (12) can be moved to an arbitrary point in a forwardly and, rearwardly extending- and upwardly and downwardly extending-plane defined by the first and second arms (4) and (7). Further, by adding the angular movement of the turntable (2), it can be moved to an arbitrary point in a space area including right and left directions, thus enabling various operations.
Next, in FIG. 3, numeral (15) denotes a first bracket fixedly secured to the base (3) and fixedly mounting the first motor (6) on the base (3) in a projecting manner. Numeral (16) denotes a first motor shaft which is an output shaft of the first motor (6). Numeral (18) denotes a first wave generator which cooperates with a first circular spline and a first flex spline later described to constitute a speed reducer commonly referred to as "harmonic drive component", and is fixedly mounted on the first motor shaft (16). Numeral (19) denotes the first circular spline fixedly mounted on the first bracket (15) coaxially with the first motor shaft (16). Numeral (20) denotes the first flex spline, and numeral (21) a first arm drive shaft, and numeral (22) a first bearing. The first arm drive shaft (21) is fixed to one side of the first arm (4), and the first bearing (22) supported by the first bracket (15) enables the first arm (4) to be swingingly moved about the same axis as that of the first motor shaft (16). The first flex spline (20) is disposed coaxially with the first circular spline (19), and is fixedly secured to the first arm drive shaft (21) at such a position that the teeth of these two splines are in mesh with each other. Numeral (23) denote a first bearing cover which holds the first bearing (22) within the first bracket (15).
Numeral (24) denotes a second bracket which is fixedly mounted on the base (3) at the side thereof opposite to the first bracket (15), with the first arm (4) interposed therebetween, the second bracket being fixed to the base (3) in such a manner that its inner periphery is disposed in coaxial relation to the first arm drive shaft (21) for the first arm 4. Numeral (25) denotes a second bearing which comprises a tapered roller bearing and is interposed between the second bracket and a sleeve-like shaft (26) fixed to the other side of the first arm (4) to support the first arm (4) in such a manner that the first arm is angularly movable relative to the second bracket (24). Numeral (27) denotes a second bearing cover which is threadedly engaged with a threaded portion (28) formed on the second bracket (24) to hold an inner ring of the second bearing (25) and also to apply a preload thereto. The second motor (11) and the first motor (6) are oppositely disposed on the same axis with respect to the first arm (4). Numeral (29) denotes a third bracket which is fixedly secured to the second bracket (24) and supports the second motor (11) in a projecting manner. Numeral (30) denotes a second motor shaft which is an output shaft of the second motor (11). Numeral (31) denotes a second wave generator fixedly mounted on the second motor shaft (30). Numeral (32) denotes a second circular spline which is fixedly mounted on the third bracket (29) coaxially with the second motor shaft (30). Numeral (33) denotes a second flex spline which is disposed coaxially with the second motor shaft (30) and cooperates with the second wave generator (31) and the second circular spline (32) to constitute a harmonic drive speed reducer. Numeral (34) denotes a second arm drive shaft, numeral (35) a third bearing, and numeral (36) a fourth bearing. The second arm drive shaft (34) is supported at opposite ends thereof by the first arm (4) through the third and fourth bearings (35) and (36), and at the intermediate portion thereof, the arm support (10) is swingingly movable about the same axis as that of the second motor shaft (30). The third and fourth bearings (35) and (36) comprises an angular contact ball bearing.
The operation will now be described.
When the first motor (6) is driven, the rotation of the first arm drive shaft (21) is reduced through the first harmonic drive speed reducer, so that the first arm (4) is swingingly moved about the axis of the first motor shaft (16). When the second motor (11) is driven, the rotation of the second arm drive shaft (34) is reduced through the second harmonic drive speed reducer, so that the link support (10) is swingingly moved about the axis of the second motor shaft (30). As mentioned above, the arm support (10) cooperates with the second arm (7), the first arm (4) and the link (9) to constitute the parallel link. Therefore, when the second motor (11) is driven, the second arm (7) is swingingly moved to operate the robot. In order to ensure the accuracy and rigidity of the robot, in the articulated portions shown in FIG. 3, the preload adjusting control is effected by a threaded adjustment of the bearing cover (27) and other means.
The drive mechanism for the articulated portions of the conventional articulated robot is constructed as described above, and therefore the number of the component parts is large, and besides in order to ensure the accuracy of the robot, it is necessary to enhance a machining precision of each component part. In addition, as mentioned above, the preload adjustment and so on are needed at the time of the assemblage. Therefore, it has been difficult to obtain robots of a high precision at low costs. Particularly, in the harmonic drive speed reducer, the arms are susceptible to vibration unless each component part is mounted on the same axis with high accuracy, and in the conventional example in which the number of the component parts is large, and a right and left-divided construction is used, a problem has been encountered that it is quite difficult to ensure a high accuracy assemblage in a stable manner.
The present invention has been made to overcome the above problems, and its object is to provide an articulated robot which can maintain a stable high accuracy without the need for adjustment by a skilled person at the time of the assemblage, and is inexpensive.
The articulated robot according to the present invention comprises at least two control arms, and two speed reducers provided at articulated portions of the two control arms on the same axis in opposed relation to each other, CHARACTERIZED in that the two speed reducers comprises first and second harmonic drive speed reducers which include a common circular spline fixedly secured to the articulated portion of one of the control arms, and a bracket mounted on one end of the common circular spline for angular movement relative to the common circular spline and connected to the articulated portion of the other control arm.
In a preferred embodiment of the invention, a cross roller bearing is interposed between the common circular spline and the bracket.
Further, in a preferred embodiment of the invention, the other bracket fixedly mounted on a base through a cross roller bearing is mounted on the other end of the common circular spline.
Further, in a preferred embodiment of the invention, the first and second harmonic drive speed reducers are constituted as a unit by the common circular spline, first and second flex splines disposed in the common circular spline on the same axis in opposed relation to each other and meshingly engaged with the common circular spline, first and second wave generators mounted respectively within the first and second flex splines on the same axis, first and second brackets respectively supporting shafts of said wave generators through bearings, and cross roller bearings each interposed between a respective one of the brackets and the circular spline.
Further, in a preferred embodiment of the invention, the shafts of the first and second wave generators are connected by respective toothed belt transmission mechanisms to output shafts of motors disposed rearwardly of or below the two control arms.
Further, in a preferred embodiment of the invention, brake devices are mounted on the shafts of the first and second wave generators, respectively.